1. Field of the Invention:
The present invention relates to a multilayer plastic pipe having improved barrier action against diffusion of the material being transported by the pipe, while maintaining dimensional stability and mechanical strength.
2. Discussion of the Background:
Plastic pipes prepared from polyamide resin are known and are used for various applications. In order to perform the particular application desired, the pipes must be inert to the material flowing in them. Additionally, they must be resistant to both high and low temperatures and mechanical stresses.
Single-layer pipes are not always capable of meeting these necessary requirements. For example, during transportation of aliphatic or aromatic solvents or fuels, they exhibit several problems, such as a lack of barrier action against the medium, dimensional instability and insufficient resistance to mechanical stresses.
Attempts have been made to solve these problems by the use of multilayer pipes (DE-A 35 10 395; 37 15 251; 38 21 723; 38 27 092; 40 01 125; and 40 01 126). However, in practice, while these multilayer pipes can solve these problems individually, the overall set of properties displayed by the pipes is still unsatisfactory.
In particular, one of the primary problems left unsolved by the above-mentioned multilayer pipes is how to adequately reduce the permeation of the pipe by methanol-containing fuels. Due to the constant reduction of legally permitted emission values, the ability to reduce this permeation by methanol fuels is of critical importance.